Air pollution is a major public health hazard, contributing to several million premature deaths annually worldwide. Air pollution directly promotes cardiovascular and respiratory diseases, and can trigger or exacerbate asthma and allergy attacks, and has been found to impair brain and lung development in children. Air pollution comprises several classes of toxic constituents. The most important components of air pollution as public health hazards are particulate matter and oxidizing gases, especially nitrogen dioxide, sulfur dioxide and ozone. Additional air pollution constituents that represent health hazards in some environments include combustion products, including carbon monoxide and carcinogenic polycyclic aromatic hydrocarbons (PAHs); volatile organic compounds (VOCs) including formaldehyde; inorganic volatiles such as mercury vapor, ammonia; allergens; and odorants such as hydrogen sulfide and sulfhydryl compounds.
Much of the analysis of health risks of air pollution has focused on particulate matter, especially particles with diameters on the order of 2.5 microns or less (PM2.5), as particles in this size range are inhaled more deeply into the airways and lungs than particles of other sizes. Particulate matter may contain toxins or carcinogens and may also provoke inflammatory responses in the airways by delivering allergens or irritants that activate macrophages or eosinophils.
In addition to particulate matter, non-particulate compounds, notably oxidizing gases, especially nitrogen dioxide, sulfur dioxide and ozone, are gaining recognition as harmful constituents of air pollution. These oxidizing gases are produced by fuel combustion whenever air is used as an oxidant, and are particularly concentrated in urban environments. Internal combustion engines, particularly diesel engines, and fossil fuel-fired electricity generation are primary sources. In enclosed spaces, cooking with combusted fuels, including wood, propane, butane and natural gas, is a significant source of nitrogen dioxide.
Oxidizing gases can react with proteins, lipids and other classes of molecules on cells in the respiratory tract and cardiovascular system.
Nitrogen dioxide is a brown gas that contributes to the visual appearance of smog in air pollution over cities or industrial areas. When nitrogen dioxide was examined as a risk factor, the number of total annual deaths attributable to air pollution were almost twice as high as previously presumed, of which data are based only on particulate matter. Nitrogen dioxide is implicated as a causal factor in strokes, lung disease, sudden infant death, and cardiovascular disease. Its reactivity and harmfulness are exacerbated by concurrent exposure to other constituents of air pollution including ozone, a radical initiator in the presence of sunlight, causing more-than-additive damage to biomolecules.
In specific environments, volatile compounds that are formed from combustion and industrial processes, in waste material, or by electrical sparks may be particularly concentrated, representing serious hazards to workers or observers. Indoor air pollution in poorly ventilated kitchen environments is a serious health hazard. Commuters are exposed to oxidizing gases and other pollutants from vehicles. Military armored vehicles can have extremely high interior concentrations of oxidizing gases, with nitrogen dioxide measured at transient peaks as high as 1000 parts per million (ppm). Air surrounding airports has high concentrations of nitrogen dioxide and other pollutants released during fuel combustion. Second hand smoke produced by combustion of tobacco products presents a local hazard; urban air pollution and tobacco smoke share some hazardous constituents in common, including polycyclic aromatic hydrocarbons, nitrogen dioxide, carbon monoxide and volatile organic compounds.
Existing personal respiratory protection devices for ordinary use, such as face masks or air filters, are able to capture particulate matter by mechanical filtration, but do not prevent inhalation of oxidizing gases or other non-particulate toxic volatile compounds. There exists a need for personal protection device, including masks or filters that neutralize or inactivate non-particulate airborne or volatile compounds including oxidizing gases, in addition to capturing harmful particulate matter.